Observational and Thermodynamic aspects of one-dimensional Dark Energy EoS parametrization models

Abstract

We examine the observational viability and physical implications of the Gong-Zhang (GZ) dark--energy equation-of-state parametrizations using exclusively late-time cosmological probes. Two one-dimensional parametrization models, GZ-Type~I and GZ-Type~II, are constrained with Type~Ia supernovae (Union3, Pantheon+SH0ES, and DES-SN5YR), DESI baryon acoustic oscillations, and cosmic chronometer measurements of $H(z)$. Bayesian inference combined with information-criteria diagnostics shows that both parametrizations provide competitive alternatives to $Λ$CDM, while the GZ-Type~II model is consistently favored, exhibiting reduced parameter degeneracy and stronger Jeffreys-scale support. Beyond background expansion tests, we employ configuration entropy as a thermodynamically motivated probe of structure formation. We demonstrate that the entropy-production rate sensitively traces the impact of dynamical dark energy on late-time gravitational clustering while preserving standard early-time behavior. Our results establish the Gong-Zhang framework as a physically transparent and observationally consistent extension of $Λ$CDM, with configuration entropy providing a complementary diagnostic of late-time cosmic acceleration.

Figures (15)

• Figure 1: Marginalized one-- and two--dimensional posterior distributions obtained from three SN+BAO+OHD dataset combinations for the Gong--Zhang Type I (left) and Type II (right) models.
• Figure 3: Jeffreys–scale comparison of GZ models against $\Lambda$CDM across datasets.
• Figure 4: Marginalized constraints on the Gong--Zhang dark--energy models. Panels (a,c) show the $68\%$ and $95\%$ confidence contours in the $\Omega_m$--$w_0$ plane, while (b,d) display the corresponding one--dimensional posteriors of $w_0$ for different SN+BAO+OHD combinations.
• Figure 5: Cosmographic corner plots showing the marginalized posterior distributions and parameter correlations for the GZ1 (left) and GZ2 (right) models.
• Figure 6: Adiabatic sound speed squared $c_s^2$ for the Gong--Zhang Type I (left) and Type II (right) models. Shaded regions denote the stable and causal domain $0<c_s^2<1$ in $(z,\omega_0)$ plane, bounded by the curves $c_s^2=0$ and $c_s^2=1$.